docs: def _parse_rs_map_file(rsfile):
          """
          Parses rsID mapping file from dbSNP
          Outputs dict where keys are coordinates in the format
          {chromsome}-{position}
  
          {
              chr1-1234: [
                  {
                      'type': 'snp'
                      'rs_id': 'rs1234'
                      'alleles': 'A/G/T'
                  }
              ]
          }
  
          :param file: file path
          :param limit: limit (int, optional) limit the number of rows processed
          :return: dict
          """
          rs_map = {}
          col = ['chromosome', 'position', 'rs_id', 'var_type', 'alleles']
          if os.path.exists(os.path.join(os.path.dirname(__file__), rsfile)):
              with open(os.path.join(os.path.dirname(__file__), rsfile)) as tsvfile:
                  reader = csv.reader(tsvfile, delimiter="\t")
                  for row in reader:
                      chromosome = row[col.index('chromosome')]
                      position = row[col.index('position')]
                      # rs_id, var_type, alleles) = row
                      map_key = "chr{0}-{1}".format(chromosome, position)
                      rs_info = {
                          'type': row[col.index('var_type')],
                          'rs_id': row[col.index('rs_id')],
                          'alleles': row[col.index('alleles')]
                      }
                      if map_key in rs_map:
                          rs_map[map_key].append(rs_info)
                      else:
                          rs_map[map_key] = [rs_info]
          return rs_map